Handwriting and Drawing are two different means of human information
storage and communication, produced by the same single two-dimensional
output system: a pointed writing implement, usually driven by the arm,
which leaves a visible trace on a flat surface. Handwriting conveys
symbolical data, whereas Drawing conveys iconic data. The third data type,
Pen Gestures, consists of unique symbols, as used by book editors and in
pen computers, requiring a function to be executed. Contrary to speech,
handwriting is not an innate neural function, and must be trained over
several years. During the training process, handwriting evolves from a slow
feedback process involving active attention and eye-hand coordination to a
fast automatic and ballistic process. The atomic movement unit in
handwriting is a stroke, which is a movement trajectory bounded by two
points of high curvature and a corresponding dip in the tangential movement
velocity. The typical modal stroke duration is of the order of 100 ms, and
varies less for increased movement amplitudes than one would expect: For a
large range, writers exert an increased force in order to maintain a
preferred rhythm of movement (10 strokes/s, 5 Hz). Once ``fired''
cortically, such a stroke cannot be corrected by visual feedback. The
handwriting process evolves in a continuous process of concurrent planning
and execution, the planning process being 2--3 characters in advance of the
execution process. Writing errors convey the fact that during writing
several processes take place, including phonemic-to-graphemic conversion
(spelling), and graphemic-to-allographic conversion (``font choice'').

Table E.1 gives an overview of parameters that may be
controlled with a pen.